Most automated sorting operations are three step processes: (1) choosing the part to be tested out of a feeder and placing it on a tester; (2) testing the part; and (3) placing the tested part into one bin if the part passes the test, or placing it into another bin if it does not pass the test. Linear actuators, such as linear motors (or forcers), are well suited for such sorting applications. A grasping end, or other grabbing device, can be mounted on a linear motor head for picking up the part to be tested. The motor can be moved over an input site where it can select a part and move it to another location for testing. Once in the tester, the part can be tested and then taken to its corresponding bin determined on the basis of the test results. This method works for most sorting processes. However, when sorting parts such as chip carriers, even the fastest linear motors cannot develop high enough throughput to keep up with the speed of the tester.
Moreover, holding the part to be tested (e.g., integrated circuit chip carriers or hybrid modules) presents some additional problems. Holding integrated circuit chip carriers or hybrid modules in test nests is usually accomplished by a four-bar clamping mechanism. Generally, a push block is attached to an end of the clamping mechanism for holding the chip during testing. The holding force is set by manually adjusting the height of this block. Such push blocks are custom built for the particular part to be tested. Manufacturing variations and wear on the four bar linkage pivots cause wide variations in the pressure exerted on the part being tested. These variations contribute to electrical repeatability problems.